Abstract
Hot water extraction (HWE) removes hemicellulose from woody biomass to give improved end products while producing a sugar-rich by-product stream, which requires proper treatment before disposal. Hot water extracted Norway spruce (Picea abies) at two different pretreatment conditions (140 °C for 300 min (H140) and 170 °C for 90 min (H170)) generated hydrolysate as a by-product, which was used in mesophilic anaerobic digestion (AD) as substrate. H140 gave a higher methane yield (210 NmL/g COD—chemical oxygen demand) than H170 (148 NmL/g COD) despite having a lower concentration of sugars, suggesting that different levels of inhibitors (furans and soluble lignin) and recalcitrant compounds (soluble lignin) affected the methane yield significantly. Organic loads (OLs) had a negative effect on the methane yield, as observed during AD of H170, while such an effect was not observed in the case of H140. This suggests that the decrease in methane yield (32%) of H170 compared to H140 is primarily due to inhibitors, while the decrease in methane yield (19%) of H140 compared to the synthetic hydrolysate is primarily due to recalcitrant substances. Therefore, both OL and pretreatment conditions must be considered for efficient anaerobic digestion from hydrolysate for enhanced methane production.
Highlights
Lignocellulosic woody biomass is used for various products, such as wood composites, board products, and biochar [1,2]
Higher sugar concentration leads to higher concentrations of furfural (0.9 g/L) and HMF (0.5 g/L) in H170 compared to 0.2 g/L of both furfural and HMF in H140
Hot water extraction (HWE) is an efficient pretreatment method to extract hydrolysate from Norway spruce to use as feed for anaerobic digestion (AD)
Summary
Lignocellulosic woody biomass is used for various products, such as wood composites, board products, and biochar [1,2]. Different pretreatment methods, such as mechanical, chemical, biological, physiochemical, and hydrothermal, are in use to make woody biomass more suitable for end products [1] Among these methods, HWE is a common hydrothermal pretreatment carried out in the temperature range 120–230 ◦ C and pressure conditions at which water is kept in subcritical condition [3]. Since the hydrolysate is rich in pentose sugar, it is not considered suitable for bioethanol production, due to the requirement of genetically modified microorganisms to degrade pentose, and these are highly sensitive to furan inhibitors like furfural and hydroxyl methyl furfural (5-HMF) present in the hydrolysate [11,12] It has been considered for the production of hydrogen through dark fermentation, but without promising results [13,14]
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